Device and method for controlling the exterior aspect of fuel rods for nuclear reactors

ABSTRACT

The invention concerns a device ( 1 ) for controlling the exterior aspect of fuel rods ( 2 ) for nuclear reactors, said device comprising optical means ( 40 ) having at least one camera ( 42, 42 ′) and linked to an image acquisition and processing system ( 48 ) capable of detecting geometric defects present on each rod ( 2 ) to be controlled, and further comprising a roughness tester ( 50 ) controlled in such a way as to measure the depth of each geometric defect detected by the image acquisition and processing system ( 48 ).  
     Moreover, the invention further concerns a method capable of being implemented with the aid of said device ( 1 ).

TECHNICAL FIELD

The present invention concerns, in a general manner, the field ofcontrolling the exterior aspect of fuel rods for nuclear reactors and,more specifically, the field of devices and methods for controlling theexterior aspect of fuel rods at the end of the production cycle.

STATE OF THE PRIOR ART

Typically, fuel rods for nuclear reactors are zirconium alloy claddingsin which are placed fissile materials. This type of cladding, generallyhaving a length between 3 and 5 metres and a diameter between 8 and 15mm, have a first sealed end and a second open end, said second end beingsealed by means of a cap welded onto the cladding, after theintroduction of the fissile materials into the interior of saidcladding.

At the end of the production of a fuel rod, it is normally necessary forits exterior surface, overall cylindrical and of circular section, tohave a satisfactory surface condition, for example of the “polishedmirror” type.

Thus, in order to control the exterior aspect of a rod when it leavesproduction, a detection is carried out for several types of defects overthe whole of the exterior surface of the rod including, notably, theexterior surface of the end cap.

Among the defects searched for, in first place are geometric defects,which may be assimilated to three dimensional defects present on theexterior surface of the rod.

By way of illustrative examples, the geometric defects may take the formof longitudinal or circumferential grooves on the exterior surface ofthe rod, whereby said grooves may be considered as defects when theyattain a depth greater than 25μ. Moreover, the defects may also take theform of impacts, caulking or even stripping off of material, still onthe said exterior surface of the rod.

The control of the exterior aspect of a fuel rod further consists indetecting cleanliness defects, said defects generally being in the formof traces of oil or foreign bodies on the exterior surface, or even inthe form of black or coloured marks with a surface area greater than adetermined value.

Finally, a third category of defect to be detected concerns apparentdefects in the end cap weld. Said type of defect, which may be presenton the weld bead of said end cap, may be in the form of pitting,blisters, cracking, overflows, shortages, sags or even colouring defectsin the weld bead.

A solution is known from the prior art that aims to control the exterioraspect of fuel rods at the end of production, through the intermediaryof a qualified operator working with the naked eye and without anymeasurement tool at his disposal.

Indeed, the fuel rods at the end of production are typically arrangedhorizontally on a stand, in bundles of thirty two elements. Onceinstalled, they are then capable of being rotated around their own axeslongitudinally by means of a friction drive mechanism, so that theoperator can control all of the exterior surfaces of said rods. In thisrespect, it is noted that tangential lighting, which may be intensityadjusted, facilitates the detection of defects by the qualifiedoperator.

However, during exterior aspect control operations, a lead glass screenmust be provided between the rods and the operator, with the obvious aimof protecting said operator against the irradiation emitted by the fuelrods. Accordingly, a major disadvantage relating to the presence of thescreen is that it has a thickness of around 100 mm and that,consequently, it is not completely translucent. Moreover, an increase inthe extent of scratching on said screen over time considerably restrictsthe operator's view.

Under these conditions, the evaluation of certain defects such as thesurface area of stains, the depth of grooves or even the evaluation ofthe colouring of weld beads becomes relatively difficult to perform.Thus, if the operator has any doubts, the rod in question is put asidein order to be recontrolled by another operator, which results directlyin a significant waste of time and a not insignificant increase in thecost of producing the rods.

It is also pointed out that the implementation of this exterior aspectcontrol technique has disadvantages directly linked to the presence ofthe operator not equipped with measurements means.

In effect, in the case of defects for which the size, depth or colouringneeds to be evaluated, the resulting verdict is, to a great extent,determined by the experience and tiredness of the operator, histiredness nevertheless being increased by the wearing of protective leadapron and the extreme and permanent attention that this type of controlstation requires. Consequently, particularly when a geometric defect hasbeen detected by the operator but his assessment of the depth ismistaken, said operator may be induced to make a false reject or, quitethe reverse, not take into consideration a defect that is, however, notacceptable.

Finally, it is pointed out that production objectives generally requirea large number of operators qualified in the field of controlling theexterior aspect of fuel rods, which naturally leads to high productioncosts.

OBJECTS OF THE INVENTION

The aim of the invention is therefore to propose a device and a methodfor controlling the exterior aspect of fuel rods for nuclear reactors,which at least partially overcomes the above mentioned disadvantages inrespect of the prior art.

More specifically, the aim of the invention is to present a device and amethod for controlling the exterior aspect of fuel rods using anappropriate tooling that makes it possible to produce a reliable, exactand repetitive verdict over time for at least part of the abovementioned defects, contrary to the solution proposed by the prior art inwhich the human verdict is subject to interpretation and risks leadingto false rejects and/or absences of detection of defects that reallydegrade the exterior aspect of the rod.

In order to achieve this, a first object of the invention is a devicefor controlling the exterior aspect of fuel rods for nuclear reactors,comprising optical means having at least one camera and linked to animage acquisition and processing system capable of detecting geometricdefects present on each rod to be controlled, and further comprising aroughness tester controlled in such a way as to measure the depth ofeach geometric defect detected by the image acquisition and processingsystem.

Advantageously, with the control device according to the invention, thedetection of geometric defects such as those described previously is nolonger carried out by means of the human eye, but automatically, throughthe intermediary of optical means such as cameras, coupled to an imageacquisition and processing system capable of detecting said type ofdefects. When a geometric defect has been detected by the imageacquisition and processing system, the roughness tester is thencontrolled in such a way that it can measure the depth of said defect,for example with the aim of comparing it to a pre-established value inorder to determine if the defect is acceptable or not.

Thus, the problems encountered in the prior art, linked to the fatigueand assessment of the operator, are totally removed, not just in thework of detecting geometric defects present on the rods but also in theoperation of evaluating the depth of said defects. Consequently, therisks of false rejects of fuel rods are practically reduced to zero,which is directly reflected by savings in terms of production costs andcontrol times.

Advantageously, it is pointed out that the optical means are capable ofscanning the exterior surface of a rod without there being anyprotective lead glass screen located between the two entities. In thisway, the device according to the invention is capable of detectinggeometric defects of very small size, even those that are difficult tosee with the naked eye.

Furthermore, the conventional processing electronics required for theproper operation of the device can easily be moved from the sensitivezone, in such a way that it is consequently not subjected to theirradiations emitted by the fuel rods.

Moreover, the control device according to the invention, preferablyintended to control the exterior aspect of rods at the end of theproduction cycle, is capable of operating continuously, withoutrequiring qualified operators.

Again advantageously, the presence of the optical means and theroughness tester near to the fuel rods only takes up very little space.

In this respect, it is pointed out that the measurement precisioncapable of being procured by a conventional roughness tester, forexample an optical roughness tester, is completely adapted to thatrequired for the present needs. Moreover, said measurement devicesadvantageously do not require contact with the rod to carry out themeasurements of the depths of the geometric defects, nor even thepresence of hydrogenated material between said measurement device andthe rod, said configuration being in any case totally excluded forobvious reasons of safety/criticity.

Furthermore, it is pointed out that the device according to theinvention may advantageously employ the optical means and the imageacquisition and processing system in order to detect other types ofdefects than geometric defects. Indeed, the image acquisition andprocessing system is of the two dimension processing software type, andis therefore perfectly capable of detecting all cleanliness defects suchas the presence of traces of oil and foreign bodies on the exteriorsurface of a rod, or even the presence on said same surface of black orcoloured marks of surface areas greater than a determined value.

In the same way, the system is also capable of detecting all of theaspect defects of the end cap weld, such as pitting, blisters, cracking,overflows, shortages, sags or even colouring defects in the weld bead.

Preferentially, the control device comprises:

-   -   a displacement stand on which may be placed a platform equipped        with a plurality of fuel rods arranged substantially parallel        alongside each other, said platform being arranged on the stand        in such a way that the rods are laid out parallel to a        longitudinal direction of said stand,        -   a trolley capable of being displaced parallel to the            longitudinal direction of said displacement stand,        -   an inspection and measurement head support mounted on the            trolley and capable of being displaced in relation to said            trolley parallel to a transversal direction of said            displacement stand,        -   an inspection and measurement head comprising at least the            optical means and the roughness tester,        -   means of rotating the fuel rods, capable of rotating each of            the rods along their own longitudinal axes,        -   an electronic and computer assembly comprising notably said            image acquisition and processing system, and        -   a coding ruler provided on the displacement stand and            capable of delivering, to the electronic and computer            assembly, the position of the trolley in relation to said            stand.

Advantageously, this specific arrangement makes it possible to control aplurality of rods placed, for example, in bundles and horizontally andfor this to be done automatically by means of the electronic andcomputer assembly that is preferentially provided so as to be able tocontrol all of the displacements and the actions of the various elementsmaking up the device. In this respect, it is notably pointed out thatthe presence of the coding ruler on the displacement stand makes itpossible to perfectly locate the detected defects, this then allowingprecise displacements and positioning of the roughness tester, so thatsaid roughness tester can measure the depths of the different geometricdefects detected.

Preferably, for each rod, the optical means are capable of carrying outa scan of the exterior surface of the rod by a plurality ofdisplacements of the trolley along the length of the rod concerned, eachdisplacement being carried out for a given angular position of the rod.Consequently, by judiciously adjusting the various angular positions ofthe rod concerned, it is easily possible to scan the whole of theexterior surface of said rod by carrying out several backward andforward movements with the trolley, each backward and forward movementthen being intended for the inspection of a specific angular section ofsaid exterior surface.

Moreover, one can provide that, during a scan of the exterior surface ofa rod, the optical means are capable of delivering a plurality of imagesto the image acquisition and processing system, each image deliveredfrom the rod being associated with an address indicating the angularposition of said rod and the position of the trolley in relation to thedisplacement stand.

Preferably, as mentioned previously, when at least one geometric defecthas been detected on a rod by the image acquisition and processingsystem, the electronic and computer assembly is capable of provoking,thanks to the addresses associated with the images delivered by theoptical means, the displacement of the roughness tester in such a waythat it can measure the depth of each geometric defect detected.

The optical means preferably comprise a plurality of primary cameras anda plurality of secondary cameras, said primary and secondary camerasbeing charge coupled devices (CCD cameras) and each being capable ofsimultaneously scanning at least two adjacent fuel rods.

Again in a preferred manner, the primary cameras and the secondarycameras are mounted on a plate assembled on the inspection andmeasurement head support, and the secondary cameras are arranged in sucha way as to be able to scan a truncated surface of an end cap of each ofthe fuel rods to be controlled, when said rods are rotated.

Moreover, the roughness tester is preferentially mounted on a liftingplate assembled on the inspection and measurement head support in such away that the roughness tester can be brought closer to each rod to carryout the measurement of the depth of each geometric defect detected.

In a preferred embodiment of the present invention, the inspection andmeasurement head further comprises diode detectors and lighting rampsthat make it possible to detect cleanliness defects, such as traces ofoil, present on each fuel rod to be controlled. Consequently, said diodedetectors can, if necessary, be used to detect traces of oil that aredifficult to detect with the aid of the previously described opticalmeans and coupled to the image acquisition and processing system.

Naturally, the association between the diode detectors and the lightingramps could also be used to assure the detection of any other elementlikely to substantially modify the light reflection produced by the rodsconcerned.

Finally, one can provide that the electronic and computer assemblycomprises information means capable of delivering and/or memory storing,for each rod controlled, a result file of the control-carried out. Byway of indicative examples, this result file may, for example, indicate“pass”, “fail” or “to be recontrolled”, as well as the address and/orimage of the defect(s) detected in the two latter cases.

A further object of the invention is a method for controlling theexterior aspect of fuel rods for nuclear reactors, comprising thefollowing steps:

-   -   detection of geometric defects present on each rod to be        controlled, with the aid of optical means having at least one        camera and linked to an image acquisition and processing system,        and    -   measurement of the depth of each geometric defect detected        during the detection of geometric defects step, with the aid of        a roughness tester.

Preferentially, for each rod, the geometric defect detection stepcomprises a scanning operation of the exterior surface of the rod withthe aid of the optical means, the scanning operation being carried outby a plurality of displacements of the optical means along the length ofthe rod concerned, each displacement being carried out for a givenangular position of each rod.

During the scanning operation of the exterior surface of a rod, theoptical means preferably deliver a plurality of images to the imageacquisition and processing system, each image delivered from the rodbeing associated with an address indicating the angular position of saidrod and the position of a trolley on which are mounted the opticalmeans, in relation to a displacement stand.

Preferably, when at least one geometric defect has been detected on arod by the image acquisition and processing system, a displacement ofthe roughness tester is carried out, thanks to the addresses associatedwith the images delivered by the optical means, in such a way that itcan measure the depth of each geometric defect detected.

Preferably, the measurement of the depth of each geometric defectdetected is carried out by bringing closer the roughness tester to therod concerned.

Furthermore, one can provide that the scanning operation of the exteriorsurface of the rods is carried out by means of a plurality of primarycameras and a plurality of secondary cameras, said primary and secondarycameras being cameras with a charge coupled device, and eachsimultaneously scanning at least two adjacent fuel rods.

In a preferred embodiment of the present invention, the control methodfurther comprises an operation of detecting cleanliness defects presenton each fuel rod to be controlled, such as traces of oil, the operationbeing carried out by means of diode detectors and lighting ramps.

Finally, the method preferably comprises a delivery step, for each rodcontrolled, of a result file of the control carried out.

Other advantages and characteristics of the invention will becomeclearer on reading the non-limitative description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with respect to the appended drawings,among which:

FIG. 1 represents a top view of a device for controlling the exterioraspect of fuel rods, according to a preferred embodiment of the presentinvention,

FIG. 2 represents a frontal view of the control device represented inFIG. 1,

FIGS. 3 a to 3 c each represent a side view, on a larger scale, of apart of the control device represented in FIGS. 1 and 2, schematicallyshowing various operations carried out during an exterior aspect controlof fuel rods, and

FIG. 4 represents a side view, on a larger scale, of a part of thecontrol device represented in FIGS. 1 and 2, schematically showing anoperation of detecting traces of oil on the fuel rods.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In reference both to FIGS. 1 and 2, a device 1 for controlling theexterior aspect of fuel rods 2 for nuclear reactors (not shown)according to a preferred embodiment of the present invention isrepresented.

It is pointed out that said device 1 is intended to allow the carryingout of an aspect control of the exterior surface 2 a of the rods 2, atthe end of the production cycle of said rods 2. Thus, the device 1 isdesigned in such a way as to verify the surface condition of theexterior surface 2 a of the rods 2 and is therefore capable of detectingthe presence of any unacceptable defects in respect of the necessaryquality requirements, the searched for defects being the same types asthose detailed above in the state of the prior art section.

In this respect, it is pointed out that the expression “exterior surface2 a” of a rod 2 is understood to comprise the exterior surface of aprincipal cladding 3 of the rod 2, a weld bead 4 linking the principalcladding 3 to an end cap 6, and the exterior surface of said end cap 6,as is, notably, represented in FIG. 3 a. It is pointed out that atruncated surface 68 of the end cap 6, normally called the end surfaceof the cap 6, forms an integral part of the exterior surface 2 a of arod 2.

In FIGS. 1 and 2, one can see that the device 1 comprises a displacementstand 8, said stand being essentially constituted of a frame 10 mountedon feet 12 fastened to the ground 14. The frame 10, of a substantiallyrectangular shape, preferentially lies parallel to the ground 14 andextends longitudinally along a longitudinal direction of the stand 8,represented by the double arrow 16 in FIG. 1, and transversally along atransversal direction of the stand 8, represented by the double arrow 18in said figure.

Thus, the frame 10 of the displacement stand 8 defines a flat surface20, substantially horizontal and parallel to the ground 14, on which maybe placed a plate 22 equipped with a plurality of rods 2, said rodsbeing arranged substantially parallel alongside each other. Moreover,the plate 22 on which the fuel rods 2 are lying at the end of theirproduction cycle, for example in such a way as to form a bundle ofthirty two elements, is brought to the stand 8 in such a way that saidrods 2 are arranged parallel to the longitudinal direction 16 of thestand 8, and thus substantially parallel to the flat surface 20 of theframe 10. It is also pointed out that a rectangular position 23,specifically dimensioned to receive the plate 22, is provided at thelevel of the flat surface 20 of the frame 10. In this way, the plate 22is capable of occupying a precise position in relation to the stand 8,said precise position being a key aspect in the proper unwinding of theoperations of controlling the exterior aspect of the rods 2.

Furthermore, the displacement stand 8 of the device 1 comprises twobeams 24 extending substantially parallel to the longitudinal direction16 of the stand 8, and being located on either side of the rectangularposition 23. On each of said beams 24 is placed a running rail 26 thatenables the displacement of a trolley 28 parallel to the longitudinaldirection 16 of the stand 8.

As can be seen in FIG. 1, the running rails 26 have a longer length thanthat of the plate 22, in order to allow the freeing of the trolley 28and, as a result, to assure a good control of the truncated surface 68of the end caps 6 of the fuel rods 2, as will be described hereafter.

The trolley 28 of the control device 1 is therefore capable of beingdisplaced along the running rails 26 of the stand 8, preferentially bymeans of a step motor and a toothed belt (not shown), said motor beingcontrolled by control means 32 forming an integral part of an electronicand computer assembly 30, the principal function of which lies in thetotal automation of the control device 1. Obviously, the assembly 30 maycomprise conventional elements such as computers, multiplexers or evensupply modules, which consequently will not be further described due totheir commonplace nature for those skilled in the art. On the otherhand, the elements of the assembly 30 specific to the present inventionwill naturally be described hereafter.

The displacement stand 8 is equipped with a coding ruler (not shown)that makes it possible to deliver, to the electronic and computerassembly 30, preferably continuously, the position of the trolley 28 inrelation to said displacement stand 8.

A support 34 for an inspection and measurement head 36 is mounted on thetrolley 28 of the device 1, as is clearly illustrated in FIGS. 1 and 2.In said figures, one can indeed see that the support 34 is lying on therunning rails 38 extending substantially parallel to the transversaldirection 18 of the stand 8, in such a way that said support 34 is thencapable of being displaced parallel to this same direction, in relationto the trolley 28.

With this specific arrangement and by carrying out judiciousdisplacements of the support 34 in relation to the trolley 28 and ofsaid trolley 28 in relation to the displacement stand 8, it is thereforeobvious that the inspection and measurement head 36 is capable ofcovering the totality of the upper surface formed by the rods 2 lying inbundles of thirty two elements on the plate 22.

Here again, it is pointed out that the displacement of the support 34 onthe trolley 28 is preferentially carried out by means of a step motorand a toothed belt (not shown), said motor preferably being controlledby the control means 32 of the electronic and computer assembly 30.

The inspection and measurement head 36, integral with the support 34,comprises optical means 40 that preferentially take the form of aplurality of charge coupled device cameras 42, 42′. In the preferredembodiment described and represented in FIGS. 1 and 2, the optical means40 comprise four primary cameras 42 and four secondary cameras 42′.Moreover, it is pointed out that said secondary cameras 42′ are intendedto scan the truncated surface 68 of the end caps 6 of the rods 2,whereas the primary cameras 42 are intended to scan the whole of theexterior surface 2 a of said rods 2, apart from said truncated surface68 of the end caps 6. In this respect, it is pointed out that thesurface inspected by the primary cameras 42 is substantially cylindricaland of circular section.

Preferably, the group of primary cameras 42 and the group of secondarycameras 42′ are each in the form of a row of cameras parallel to thetransversal direction 18, and are each intended to scan eight adjacentrods 2 at the same time. Moreover, each of said cameras 42, 42′ iseffectively adjusted to have two adjacent rods 2 in its field of view.Obviously, the number of cameras 42, 42′ and the number of rods 2 thatthey are capable of scanning at any single time may be adapted as afunction of the needs encountered, without going beyond the scope of theinvention.

The four primary cameras 42, of the progressive scan type, arepreferably mounted on a plate 44 assembled on the support 34, in such away that each optical axis 46 of a camera 42 is located substantiallyperpendicular to the two rods 2 that it has in its field of view, andsubstantially perpendicular to the flat surface 20 of the frame 10, asis clearly shown in FIG. 2.

Moreover, the four secondary cameras 42′ are preferably also mounted onsaid plate 44, but in such a way as to be capable of correctly viewingthe truncated surface 68 of the end caps 6. Thus, as is clearly shown inFIG. 3 a, the primary cameras 42 are mounted substantially vertically,whereas the secondary cameras 42′ are mounted at an angle.

The cameras 42, 42′ are capable of delivering images of the rods 2 to animage acquisition and processing system 48 to which they are linked, thetwo dimension processing software type system 48 forming an integralpart of the electronic and computer assembly 30.

Consequently, the system 48 is capable of detecting defects present onthe fuel rods 2, such as geometric defects similar to those indicatedabove in the state of the prior art section, from images delivered bythe cameras 42, 42′ and following a conventional processing of saidimages. Naturally, the image acquisition and processing system 48 isalso capable of detecting cleanliness defects such as the presence oftraces of oil and foreign bodies on the exterior surface 2 a of a rod 2,or even the presence on said surface 2 a of black or coloured marks ofsurface area greater than a determined value.

In addition, the system 48 is further capable of detecting all of theweld aspect defects of the end cap 6, such as pitting, blisters,cracking, overflows, shortages, sags or even colouring defects in theweld bead 4.

The inspection and measurement head 36 also comprises a roughness tester50, mounted on a lifting plate 52 assembled on the support 34, in such away that said roughness tester 50 is located substantially at the levelof the support 34 when the lifting plate 52 occupies a retractedposition, and in such a way that said roughness tester is located nearto the rods 2 when the plate 52 is in a projecting position. It shouldbe noted that this latter position is that adopted to carry out ameasurement of the depth of a geometric defect detected by the system48, and that this same projecting position is obtained by a displacementtowards the floor 14 of the lifting plate 52, in a substantiallyperpendicular direction to the flat surface 20 of the frame 10.

In this respect, the displacements of the lifting plate 52 arepreferentially assured by the control means 32 of the assembly 30.

Typically, the roughness tester 50 that assures the measurement of thedepth of geometric defects detected is a PERTHOMETER (registered tradename) or CONFOCAL (registered trade name) type optical sensor roughnesstester, in which the range of measurement is plus or minus 300μ.

In addition, it is pointed out that the data collected by the roughnesstester 50 is transmitted to the acquisition and processing means 51forming an integral part of the assembly 30, said means 51 then beingcapable of processing the data received in order to determine the depthof the defects detected, then transferring the depth measurements to acentral memory 55 of said assembly 30.

More specifically in reference to FIG. 1, the head 36 comprises lightingramps 54, preferably assuring a continuous and stable lighting. By wayof illustrative example, two ramps 54 may be placed parallel to thetransversal direction 18 of the stand 8, respectively on either side ofthe optical means 40.

Apart from the faculty that the ramps 54 offer to the cameras 42, 42′ totake good quality images, said ramps 54 may also be placed inassociation with diode detectors 56, integral with the support 34. Thisassociation allows the detection of cleanliness defects present on theexterior surface 2 a of the rods 2, such as traces of oil, as will bedescribed in more detail hereafter. Thus, said diode detectors 56 may,if necessary, be used to detect traces of oil that are difficult todetect with the aid of the optical means 40 described above and coupledto the image acquisition and processing system 48.

Preferably, each diode detector 56, arranged in such a way as to be ableto be positioned plumb with a fuel rod 2 on the support 34, is equippedwith a lens focusing its measurement field on the rod 2 concerned, andis capable of receiving the light emitted by the lighting ramps 54 andreflected on the exterior surface 2 a of said rod 2. In addition, thedetectors 56 are linked to a management module 57 forming an integralpart of the assembly 30, and enabling in particular the acquisition ofthe “ALL” or “NOTHING” results delivered by the detectors 56.

By way of indicative example, in the preferred embodiment of the presentinvention, the detectors 56 are placed alongside each other in such away as to form a row extending substantially parallel to the lightingramps 54, and thus substantially parallel to the transversal directionof the stand 8.

More specifically in reference to FIG. 2, it can be seen that thecontrol device 1 further comprises means of rotating 58 the rods 2, saidmeans 58 preferably being assembled on the feet 12 of the device 1.

The means 58 are vertically telescopic, in other words they can bedisplaced in relation to the stand 8 along a vertical directionrepresented by the double arrow 60 in FIG. 2, said vertical directionthus being perpendicular to the flat surface 20 of the frame 10. In thisway, by bringing into action a step motor (not shown), preferentiallycontrolled by the control means 32, it is possible to establish or tobreak the contact between the drive belts 62 of the means 58 and themeans (not shown) themselves located in permanent contact with the lowerpart of the exterior surface 2 a of the rods 2. It is pointed out thatin FIG. 2, a single drive belt 62 is visible, due to the fact that thespecific plan of this FIG. 2 implies that the other belts are hidden bythe one shown. However, the drive belts 62, preferably identical, arespaced from each other along the longitudinal direction 16, for examplearound every 400 mm.

Furthermore, the drive belts 62 are capable of being brought intomovement by means of a step motor (not shown), again preferentiallycontrolled by the control means 32, so that the upper part of said belts62 can be displaced in a direction substantially parallel to thetransversal direction 18 of the stand 8.

In this respect, it is pointed out that in a manner known to thoseskilled in the art but not represented, the rods 2 may be displaced bymeans 58 in such a way that they lie on landings on which are integratedrollers, said rollers being capable of being driven by the drive belts62. In addition, the plate 22 is pierced in order to be able to becrossed by said drive belts 62, and thus to allow the contact betweenthese and the rollers supporting the rods 2.

Thus, when the drive belts 62 are actually brought into movement and arein contact with the rollers supporting the rods 2, they then provoke therotation of all of said rods 2 along their own longitudinal axes.

In this way, it is possible to control all of the exterior surface 2 aof each rod 2 by means of the inspection and measurement head 36, bycarrying out a plurality of backward and forward movements with thetrolley 28, each backward and forward movement of the trolley 28 beingcarried out along the whole length of the rods 2 to be controlled, for agiven angular portion of said rods 2.

It is pointed out that during the delivery of an image by the opticalmeans 40 to the image acquisition and processing system 48, theelectronic and computer assembly 30 is capable of associating with saidimage an address indicating the angular position of the rod 2 concerned,and the position of the trolley 28 in relation to the displacement stand8, said position being delivered by the coding ruler as mentioned above.In addition, the images processed by the system 48, for which one orseveral defects have been detected, are capable of being transferredinto the central memory 55 of the assembly 30, while being associatedwith their respective addresses, the content of which is detailed above.

Finally, the assembly 30 of the device 1 comprises information means 66capable of delivering and/or memory storing, for each rod 2 controlled,a result file of the control carried out. As will be more fullyexplained hereafter, said result file may indicate “pass”, “fail” or “tobe recontrolled”, as well as the address and/or the image of thedefect(s) detected in the two latter cases.

The device 1 for controlling the exterior aspect that has just beendescribed is capable of operating in the preferred manner describedbelow, referring in particular to FIGS. 3 a to 3 c and to FIG. 4.

In the first instance, in referring to FIGS. 3 a to 3 c, the operationof the device 1 will be described, during the exterior aspect controloperations aiming to detect geometric defects, such as defects thatcould take the form of longitudinal or circumferential grooves on theexterior surface 2 a of the rods 2, it being possible to consider saidgrooves as defects when they attain a depth greater than 25μ. Inaddition, they may also involve impacts, caulking or even stripping offof material, still at the level of said exterior surface 2 a of the rods2.

A plate 22 of thirty two rods 2 is first transported in the direction ofthe displacement stand 8, for example in an automatic manner, in orderto be brought to the rectangular position 23 provided for this purposeon the frame 10.

In a known manner, the means of rotating 58 are then brought into actionby the control means 32, in order to free the rods from their arrivalposition, in such a way that they then lie on their associated rollers.

At this moment, the trolley 28 occupies a start position in which it isrested against the stand 8 and situated completely beyond the rods 2 inthe longitudinal direction 16, as shown by a dotted line in FIG. 1. Inaddition, the support 34 for the inspection and measurement head 36 ispositioned on the trolley 28 in such a way that said head 36 can inspectthe first eight rods 2, located at the end of the bundle of thirty twoelements.

As shown in FIG. 3 a, when the trolley 28 occupies its start position,the optical axes 46′ of the inclined secondary cameras 42′ aresubstantially perpendicular to the truncated surface 68 of the end cap6, said truncated surface 68 normally being called the end surface ofthe cap 6 and forming an integral part of the exterior surface of saidcap 6. In addition, the truncated surface 68 has a principal axisidentical to a longitudinal axis 74 of the rod 2. By way of illustrativeexample, the optical axes 46′ of the secondary cameras 42′ may beinclined 450 in relation to a horizontal plane parallel to the flatsurface 20 of the frame 10. In other words, the optical axes 46′ form anangle A′ of around 450 with the longitudinal axis 74 of the rods 2, in aplane perpendicular to the ground 14.

An image is then taken by each of the four secondary cameras 42′, thentransmitted to the image acquisition and processing system 48, which, assoon as the images are received, begins to carry out the processing. Itshould be noted that in the preferred embodiment described, each imagetaken by a secondary camera 42′ contains the representation of a part oftwo truncated end surfaces 68 belonging respectively to two adjacentrods 2.

In parallel, the control means 32 displace the trolley 28 facing the endcap 6 in order to begin the scanning of the remainder of the exteriorsurface of said end cap 6, and that of the cladding 3 and the weld bead4 of the rods 2. In this respect, it is pointed out that the part of theexterior surface of the end cap 6 remaining to be inspected issubstantially cylindrical and of circular section, and constitutes anextension of the exterior surface of the cladding 3.

To do this, the trolley 28 is displaced on the running rails 26, alongthe whole length of the rods 2, as shown schematically in FIG. 3 b.Images are then taken regularly by the primary cameras 42, for precisepositions of the trolley 28 in relation to the stand 8, so that theupper part of the exterior surfaces 2 a of the rods 2, visible by saidsame primary cameras 42, are completely scanned. In this respect, it ispointed out that the precision of the positions of the trolley 28 iseasily assured by the coding ruler equipping the displacement stand 8.

After each image is taken, the images are directly delivered to thesystem 48, then analysed by said system 48 while the trolley 28 isdisplaced in order to return to the position in which the primarycameras have to take the following images.

In the event where one or several geometric defects are detected by thesystem 48, the corresponding images are transferred into the centralmemory 55, while being associated with their respective addressesindicating the angular-position of the rod 2 concerned, and the positionof the trolley 28 in relation to the displacement stand 8. On the otherhand, the images that have not been the subject of any detection ofgeometric defect are preferably not conserved in the memory.Nevertheless, it could be provided that they are stored for a giventime, for example of the order of several days, by storing them in acompressed manner on a recording support such as a CD-ROM.

Thus, the trolley 28 is displaced at constant speed by the control means32 up to its final position in which it rests against the stand 8, andlocated facing the ends of the rods 2 opposite the caps 6, as also shownby a dotted line in FIG. 1.

Once this final position has been attained, the control means 32 provokethe bringing into action of the means of rotating 58 the rods 2, so thatthe eight rods 2 inspected are pivoted along their own longitudinalaxes. The fuel rods 2 concerned are consequently positioned in adifferent angular position from the previous one, with the aim ofcontrolling another angular section of the exterior surface 2 a of saidrods 2.

When the rotation has taken place, the scanning of the exterior surfacesof the claddings 3 and the caps 6 and the scanning of the weld beads 4is carried out again, during the displacement of the trolley 28 from thefinal position to the start position. In the same way as previously, theimages taken by the primary 42 and secondary 42′ cameras having been thesubject of a detection of at least one geometric defect are stored inthe central memory 55.

By way of illustrative example, the means of rotating 58 are programmedso that the exterior surface 2 a of the rods 2 is entirely scannedfollowing twelve rotations. In such a case, the trolley 28 is controlledby the control means 32 in such a way as to carry out six backward andforward movements above said adjacent eight rods 2, each backward andforward movement corresponding to a given angular position of said rods2.

Once all of the backward and forward movements have been carried out bythe trolley 28 and the images of the geometric defects have beentransferred to the central memory 55 of the assembly 30, the controlmeans 32 generate displacements of the roughness tester 50 with the aimof measuring the depth of each of the geometric defects detected.

Thus, for each geometric defect detected, the trolley 28, the support 34and the means of rotating 58 and controlled by the control means 32, sothat the roughness tester 50 is placed facing the geometric defectconcerned. Obviously, said displacements are carried out as a functionof the address of the stored image containing the defect, and as afunction of the positioning of said defect on the image.

Then, the control means 32 provoke the displacement of the lifting plate52, in such a way that the roughness tester 50 is placed near to thedefect 70 detected, as shown in FIG. 3 c. By way of indicative example,the plate 52 is displaced vertically downwards in such a way that theroughness tester 50 is placed 10 mm from the defect 70 detected.

Measurements are then carried out by said roughness tester 50, whichdirectly transmits the data collected to the acquisition and processingmeans 51 so that they can determine the depth of the defect 70.

This operation is therefore repeated as many times as necessary tomeasure the depth of all of the geometric defects, the depth values thenbeing associated with the images in the central memory 55 of theassembly 30.

The control of the first eight rods 2 with regard to geometric defectsnow being completed, the trolley 28 is then displaced in its startposition such as described here above, then the support 34 is alsodisplaced in relation to the trolley 28 in such a way that the head 36can inspect the next eight rods 2, as is shown in fine lines in FIG. 2.

All of the operations described below are carried out in the same wayfor said eight new rods 2, as well as for the two other remaining setsof eight adjacent rods 2.

Again by way of illustrative example, another solution could consist inproviding that the trolley 28 is controlled by the control means 32 insuch a way that, following the inspection of the first angular sectionof the first set of eight adjacent rods 2, said trolley 28 does notinspect the second angular section of the first set, but said firstangular section of the second set of eight adjacent rods 2.

Consequently, contrary to the example described previously, the trolley28 carries out a succession of backward and forward movements in orderto inspect a same angular section of each of the thirty two rods 2 inthe bundle. Once said angular section has been fully inspected, thecontrol means 32 provoke the bringing into action of the means ofrotating 58 the rods 2, which then leads to a pivoting of all of saidrods 2 in such a way that their next angular section can in turn becontrolled by the trolley 28.

In addition, it could be provided that, during the backward and forwardmovements carried out by the trolley 28 and as soon as a geometricdefect has been detected, the control means 32 immediately generate adisplacement of the roughness tester 50, with the aim of measuring thedepth of said detected geometric defect.

Whatever the solutions retained among those detailed above, when thebundle of rods 2 is inspected, the trolley 28 is equipped with a reader(not shown) integral with the support 34, which is capable of reading abar code (not shown) present on each of said rods 2.

Thus, when the reader reads a bar code, all of the information known onthe rod 2 concerned is transferred to the information means 66 capableof delivering and/or memory storing a result file of the control carriedout.

Said result file, presenting the bar code of the rod 2, could firstlyindicate “pass” when no geometric defect has been detected by the imageacquisition and processing system 48.

Moreover, in the event where at least one geometric defect has beendetected by the system 48, the result file then preferably indicates“fail”. In this case, said file may also advantageously comprise theimages of the detected defects, associated with the respective addressesand the associated depth values.

It is pointed out that in the event where no geometric defect detectedexceeds a pre-established depth value, for example 25μ, the result filecould then indicate “to be recontrolled”, in order to determine if thepresence of the defects adversely affects or not, in a significantmanner, the quality of the surface condition of the rod 2.

The detection operations of certain cleanliness defects such as thepresence of traces of oil and foreign bodies on the exterior surface 2 aof the rods 2, or even the presence on said surface 2 a of black orcoloured marks with a surface area greater than a determined value, maybe carried out in a similar manner to that detailed for the geometricdefect detection operations, and simultaneously with these latteroperations, as with operations for detecting aspect defects in the weldbead 4 of the end cap 6, said defects can be present in the form ofpitting, blisters, cracking, overflows, shortages, sags or evencolouring defects in the weld bead.

Indeed, when the images are delivered by the primary 42 and secondary42′ cameras to the image acquisition and processing system 48, it iscapable of differentiating geometric defects from cleanliness or weldbead aspect defects. Thus, when a cleanliness or weld bead 4 aspectdefect is detected, the image associated with its address is directlytransferred to the central memory 55, but the measurement operation withthe aid of the roughness tester 50 will obviously not be ordered.

In this way, following the reading of the bar code of a rod 2, theinformation known on said rod 2 and transferred to the means ofinformation 66 may then include data concerning cleanliness or weld bead4 aspect defects of the type described above, in such a way that in sucha case, the result file of the control must indicate “fail”.

In the event where the association between the cameras 42, 42′ and theimage acquisition and processing system 48 do not prove sufficientlysatisfactory for the detection of cleanliness defects of the type of oiltraces present on the exterior surface 2 a of the rods 2, it is thenpossible to carry out a detection of this type of defect by means of thelighting ramps 54 coupled to the diode detectors 56.

Obviously, the detection by means of said lighting ramps 54 is carriedout in parallel to the abovementioned operations, using the cameras 42,42′.

Thus, as shown in FIG. 4, during the displacement of the trolley 28described above, the detectors 56 receive the light reflected on therods 2 and emitted by the ramps 54. To do this, the optical axes 72 ofthe detectors 56 preferentially form an angle A of around 60° with thelongitudinal axis 74 of the rods 2, in a plane perpendicular to theground 14.

Preferably, at the same time as the images are taken by the primary 42and secondary 42′ cameras, the management module 57 acquires the results“ALL” or “NOTHING” delivered by said detectors 56.

Consequently, when a detector 56 has in its field of view a trace of oiladhering to the exterior surface 2 a of a rod 2, the reflection is thenmore intense and the signal delivered by the detector 56 goes from“NOTHING’ to “ALL”. In this way, during the following acquisitioncarried out by the management module 57, said module 57 is informed ofthe presence of a trace of oil at a given address, and may thereforetransfer said information to the central memory 55.

Naturally, after each acquisition of the management module 57, itprovokes the return to zero of the signals generated by the diodedetectors 56.

Thus, once again, following the reading of the bar code of a rod 2, theinformation known on said rod 2 and transferred to the information means66 may then include data concerning cleanliness defects of the trace ofoil type, in such a way that in this case, the result file of thecontrol must indicate “fail”.

Moreover, it is pointed out that with the presence of the cameras 42,42′ and the image acquisition and processing system 48 and, morespecifically, with that of the primary cameras 42, it is possible toverify that each rod 2 has indeed made a complete rotation during thedefect detection operations.

Indeed, each rod 2 has an identification number inscribed several timeson the exterior surface of the cladding 3, for example four times. Saidfour identical identification numbers are thus inscribed on a samelongitudinal level of the rod 2 concerned, for example of the exteriorsurface of the cladding 3 near to the end cap 6, parallel to theirlongitudinal axis 74, and every 90° around said axis.

In this way, during the first forward movement of the trolley 28, whenit comes to be positioned at the specific level of the rods 2 where saididentification numbers are inscribed, the primary camera 42 concernedtakes an image placed in the memory of the central memory 55. On theimage obtained, the specific position of the visible identificationnumber then defines an angular start position of the rods 2.

Thus, the twelve angular control positions of the rod 2 being organisedto overlap, the comparison between the first image and the twelfthimage, theoretically identical, make it possible to determine if the rod2 has undergone or not a complete rotation. If this is not the case, oneor several additional increments may be ordered in order to inspect allof the exterior surface 2 a of the rod 2.

Naturally, said comparison of the first and the final images taken bythe primary camera 42 is carried out by means of the image acquisitionand processing system 48.

The invention also concerns a method for controlling the exterior aspectof fuel rods 2 for nuclear reactors, said method being capable of beingimplemented with the aid of the control device 1 that has just beendescribed, and comprising the principal steps consisting in detectingthe geometric defects present on each rod 2 to be controlled, with theaid of optical means 40 having at least one camera 42, 42′ and linked tothe image acquisition and processing system 48, then measuring the depthof each geometric defect detected during the geometric defect detectionstep, with the aid of a roughness tester 50.

Obviously, various modifications may be made by those skilled in the artto the device 1 and the exterior aspect control method that have beendescribed here above, uniquely by way of example and in a non-limitativemanner.

1. Device (1) for controlling the exterior aspect of fuel rods (2) fornuclear reactors, characterised in that it comprises optical means (40)having at least one camera (42, 42′) and linked to an image acquisitionand processing system (48) capable of detecting geometric defectspresent on each rod (2) to be controlled, and in that it furthercomprises a roughness tester (50) controlled in such a way as to measurethe depth of each geometric defect detected by the image acquisition andprocessing system (48).
 2. Aspect control device (1) according to claim1, characterised in that it comprises: a displacement stand (8) on whichmay be placed a platform (22) equipped with a plurality of fuel rods (2)arranged substantially parallel alongside each other, said platform (22)being arranged on the stand (8) in such a way that the rods (2) are laidout parallel to a longitudinal direction (16) of said stand (8), atrolley (28) capable of being displaced parallel to the longitudinaldirection (16) of said displacement stand (8), an inspection andmeasurement head support (34) mounted on said trolley (28) and capableof being displaced in relation to said trolley parallel to a transversaldirection (18) of said displacement stand (8), an inspection andmeasurement head (36) comprising at least the optical means (40) and theroughness tester (50), means (58) of rotating the fuel rods (2), capableof rotating each of the rods (2) along their own longitudinal axes (74),an electronic and computer assembly (30) comprising in particular saidimage acquisition and processing system (48), and a coding rulerprovided on the displacement stand (8) and capable of delivering, to theelectronic and computer assembly (30), the position of the trolley (28)in relation to said stand (8).
 3. Aspect control device (1) according toclaim 2, characterised in that for each rod (2), the optical means (40)are capable of carrying out a scan of the exterior surface (2 a) of therod (2) by a plurality of displacements of the trolley (28) along thewhole rod (2) concerned, each displacement being carried out for a givenangular position of said rod (2).
 4. Aspect control device (1) accordingto claim 3, characterised in that during a scan of the exterior surface(2 a) of a rod (2), the optical means (40) are capable of delivering aplurality of images to the image acquisition and processing system (48),each image delivered from the rod (2) being associated with an addressindicating the angular position of said rod (2) and the position of thetrolley (28) in relation to the displacement stand (8).
 5. Aspectcontrol device (1) according to claim 4, characterised in that when atleast one geometric defect has been detected on a rod (2) by the imageacquisition and processing system (48), the electronic and computerassembly (30) is capable of provoking, thanks to the addressesassociated with the images delivered by the optical means (40), thedisplacement of the roughness tester (50) in such a way that it canmeasure the depth of each geometric defect detected.
 6. Aspect controldevice (1) according to claim 1, characterised in that the optical means(40) comprises a plurality of primary cameras (42) and a plurality ofsecondary cameras (42′), said primary (42) and secondary (42′) camerasbeing cameras with a charge coupled device and each being capable ofsimultaneously scanning at least two adjacent fuel rods (2).
 7. Aspectcontrol device (1) according to claim 6, characterised in that theprimary cameras (42) and the secondary cameras (42′) are mounted on aplate (44) assembled on said inspection and measurement head support(34), and in that the secondary cameras (42′) are arranged in such a wayas to be able to scan a truncated surface (68) of an end cap (6) of eachof the fuel rods (2) to be controlled.
 8. Aspect control device (1)according to claim 2, characterised in that the roughness tester (50) ismounting on a lifting plate (52) assembled on said inspection andmeasurement head support (34) in such a way that the roughness tester(50) can be brought closer to each rod (2) to carry out the measurementof the depth of each geometric defect detected.
 9. Aspect control device(1) according to claim 2, characterised in that the inspection andmeasurement head (34) further comrpises diode detectors (56) andlighting ramps (54) that make it possible to detect cleanliness defectspresent on each fuel rod (2) to be controlled.
 10. Aspect control device(1) according to claim 2, characterised in that the electronic andcomputer assembly (30) comprises information means (66) capable ofdelivering and/or memory storing, for each rod (2) controlled, a resultfile of the control carried out.
 11. Method for controlling the exterioraspect of fuel rods (2) for nuclear reactors, characterised in that itcomprises the following steps: detection of geometric defects present oneach rod (2) to be controlled, with the aid of optical means (40) havingat least one camera (42, 42′) and linked to an image acquisition andprocessing system (48), and measurement of the depth of each geometricdefect detected during the detection of geometric defects steps, withthe aid of roughness tester (50).
 12. Method for controlling theexterior aspect according to claim 11, characterised in that for eachrod (2), the geometric defect detection step comprises a scanningoperation of the exterior surface (2 a) of said rod (2) with the aid ofthe optical means (40), the scanning operation being carried out bymeans of a plurality of displacements of the optical means (40) alongthe whole rod (2) concerned, each displacement being carried out for agiven angular position of said rod (2).
 13. Method for controlling theexterior aspect according to claim 12, characterised in that during thescanning operation of the exterior surface (2 a) of a rod (2), theoptical means (40) deliver a plurality of images to the imageacquisition and processing system (48), each image delivered from therod (2) being associated with an address indicating the angular positionof said rod (2) and the position of a trolley (28) on which are mountedthe optical means (40), in relation to a displacement stand (8). 14.Method for controlling the exterior aspect according to claim 13,characterised in that when at least one geometric defect has beendetected on a rod (2) by the image acquisition and processing system(48), a displacement of the roughness tester (50) is carried out, thanksto the addresses associated with the images delivered by the opticalmeans (40), in such a way that it can measure the depth of eachgeometeric defect detected.
 15. Method for controlling the exterioraspect according to claim 11, characertised in that the measurement ofthe depth of each geometric defect detected is carried out by bringingcloser the roughness tester (50) to the rod (2) concerned.
 16. Methodfor controlling the exterior aspect according to claim 12, characterisedin that the scanning operation of the exterior surface (2 a) of the rods(2) is carried out by means of a plurality of primary cameras (42) and aplurality of secondary cameras (42′), said primary (42) and secondary(42′) cameras being cameras with a charge coupled device, and eachsimultaneously scanning at least two adjacent fuel rods (2).
 17. Methodfor controlling the exterior aspect according to claim 11, characterisedin that it further comprises an operation of detecting cleanlinessdefects present on each fuel rod (2) to be controlled, the operationbeing capable of being carried out by means of diode detectors (56) andlighting ramps (54).
 18. Method for controlling the exterior aspectaccording to claim 11, characterised in that it comprises a step ofdelivering, for each rod (2) controlled, a result file of the controlcarried out.